镁合金激光熔凝层显微组织分析

采用激光熔凝技术处理镁合金,系统分析了激光熔凝处理后熔凝层组织变化特征。研究结果表明,激光熔凝处理后,熔凝层相组成仍为α-Mg和β-Mg17Al12,其中β相含量较原始镁合金有所提高。熔凝层组织呈明显的树枝晶形貌特征,较原始镁合金晶粒显著细化,且沿熔凝层深度增加,枝晶尺寸逐渐增大。透射电镜分析进一步证明了熔凝层由密排六方结构的α-Mg和体心立方结构的β-Mg17Al12组成,其中β相呈板条状、短柱状和六棱柱状多种形态析出。另外,当激光功率从2 kW增加到5 kW时,熔凝层中β含量和枝晶尺寸均增加,且枝晶长度方向的增加幅度约为宽度方向上增加幅度的10倍。在枝晶细化和沉淀强化综合作用下,熔凝层的耐磨性较原始镁合金有显著提高。

Analysis of the Microstructure of Laser Melting Layer on Mg Alloy

The paper uses laser melting technology to treat the Mg alloy, systemly analyzing the microstructure charactristic of the melted layer after laser melting. The results show that the melted layer is consisted of the α-Mg and β-Mg17Al12, the content of β in the melted layer is higher than that of the received Mg alloy. The microstructure of the melted layer presents the dendrite characteristic, has significantly finer than that of the received Mg alloy. With the increasing of the depth of the melted layer, the dimension of the dendrite increases. The analysis of the transmission electron microscope furtherly shows that the melted layer is composed of close-packed hexagonal α-Mg and body-centred cubic β-Mg17Al12 , β precipitates as the lath, short column and hexagonal prism morphology. Otherwise, when the laser power increases from 2 kW to 5 kW, the content of β and the dimension of the dendrite in the melted layer both increases, and the increasing extent of the length of the dendrtie is 10 times to the that of the width of the dendrtie.Under the comprehensive action of the refining dendrite and precipitation strengthening, the wear resistance of the melted layers have the significant increasing compared with that of the as-received Mg alloy.